/*
 * Copyright 2000-2017 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.util;

import org.jetbrains.annotations.Nullable;

import java.util.Collection;

/**
 * @author max
 * @see Functions for some common implementations
 * <p>
 * Consider to use java.util.function.Function
 */
@SuppressWarnings({"unchecked"})
public interface Function<Param, Result> {
    Result fun(Param param);

    Function ID = new Function.Mono() {
        public Object fun(Object o) {
            return o;
        }
    };

    Function NULL = NullableFunction.NULL;

    Function TO_STRING = new Function() {
        public Object fun(Object o) {
            return String.valueOf(o);
        }
    };

    interface Mono<T> extends Function<T, T> {
    }

    final class InstanceOf<P, R extends P> implements NullableFunction<P, R> {

        private final Class<R> myResultClass;

        public InstanceOf(Class<R> resultClass) {
            myResultClass = resultClass;
        }

        @Nullable
        public R fun(P p) {
            return p.getClass().isAssignableFrom(myResultClass) ? (R) p : null;
        }
    }

    final class First<P, R extends P> implements Function<P[], R> {
        public R fun(P[] ps) {
            return (R) ps[0];
        }
    }

    final class FirstInCollection<P, R extends P> implements Function<Collection<P>, R> {
        public R fun(Collection<P> ps) {
            return (R) ps.iterator().next();
        }
    }

}
